The present invention relates to a sensor guide wire, and in particular to a sensor guide wire provided with a polymer layer in the tip region.
Today, there is an increased need for invasive measurements of physiological variables. For example, when investigating cardiovascular diseases, it is strongly desired to obtain local measurements of blood pressure, flow and temperature in order to evaluate the condition of the subject under measurement. Therefore, methods and devices have been developed for disposing a miniature sensor inside the body of an individual at a location where the measurements should be performed, and for communicating with the miniature sensor in order to provide the physician or medical technician with critical information as to the status of a patient's condition. Typically, the miniature sensor is arranged at a distal end of a guide wire, which is generally known in the art, and used for example in connection with the treatment of coronary disease.
The distal end of the guide wire is inserted into the body of a patient, for example into an opening of the femoral artery, and placed at a desired location. Once the guide wire is placed by the physician into the appropriate location, e.g. in a coronary artery, the miniature sensor can measure the blood pressure and/or flow. The measurement of blood pressure is a way to diagnose e.g. the significance of a stenosis. For evident reasons, the dimensions of the sensor and the guide wire are fairly small; the guide wire typically has a diameter of 0.35 mm. Generally, the sensor element is in the form of an elongated, essentially rectangular chip with a pressure sensitive member in the form of a membrane provided thereon.
In order to power the sensor and to communicate signals representing the measured physiological variable to a control unit acting as an interface device disposed outside the body, one or more microcables for transmitting the signals are connected to the sensor, and are routed along the guide wire to be passed out from the vessel to an external control unit via a connector assembly. Most commonly, extremely thin electrical cables are provided inside the guide wire, which itself is provided in the form of a tube (having an outer diameter of e.g. 0.35 mm), oftentimes made of stainless steel. In order to increase the bending strength and maneuverability of the tubular guide wire, a core wire is positioned inside the tube. The mentioned electrical leads are positioned in the space between the inner lumen wall of the tube and the core wire. Furthermore, the sensor chip is often arranged in a short tube, also referred to as a jacket or a sleeve. The jacket is hollow and accommodates, besides the sensor chip, a portion of a core wire and often at least one microcable. Furthermore, a first coil may be attached to the distal end of the jacket, and optionally a second coil may be attached to the proximal end of the jacket. The first and second coils may be attached to the respective end of the jacket, e.g. by gluing, or alternatively soldering. The purpose of the first coil is to provide a tip with high flexibility. In addition, the distal coil is often designed to be radioopaque, to enable the user to locate the tip on an angiogram during use.
A large flexibility of the sensor guide wire is advantageous in that it allows the sensor guide to be introduced into small and tortuous vessels. It should, however, also be recognized that if the core wire is too flexible, it would be difficult to push the sensor guide forward into the vessels, i.e. the sensor guide wire must possess a certain “pushability” and a certain “torquability.” Additionally, the sensor guide must be able to withstand the mechanical stress exerted on the core wire especially in sharp vessel bends.
Several different designs of sensor guide wires are known in the prior art, and examples of such sensor guide wires are disclosed in U.S. Pat. No. 6,167,763 B1, which describes the cantilevered mounting of the sensor element, US RE39863 E1, which discloses the sensor element, and U.S. Pat. No. 6,248,083 B1, showing the complete sensor guide wire assembly, which all are assigned to the assignee of the present application, and which are hereby all incorporated by reference for the devices and methods described therein.
A further example of a sensor guide wire is disclosed in WO 2009/054800 A1, assigned to the present assignee. The sensor guide wire has a proximal shaft region, a flexible region, a distal sensor region, and a tip region. The tip region of the sensor guide wire is provided with a tip core wire at least partly enclosed by a distal coil.
Besides being flexible enough, it can be also important that the sensor guide wire tip responds when steering the sensor guide wire through the tortuous vessels, i.e. the sensor guide wire tip must also have sufficient “steering response.” “Steering response” is a measure of the irregular behavior of a sensor guide wire when the sensor guide wire tip is subjected to a non-linear pathway and rotated. This rotation is initiated by the user at the proximal end of the assembly, and depending on the characteristics of the different sections of the assembly, will be transferred along the wire in slightly different ways. The “steering response” of a sensor guide wire tip is a general property of the distal tip components.
The inventors of the present invention has further identified a need for a sensor guide wire with improved properties relating to the possibilities for the physician to feel constrictions and various bends and turns in the vessels when introducing the sensor guide wire. Thus, there is a need for a sensor guide wire which provides improved “sensing capabilities.”